Molybdenum sulfur-containing compounds have been proposed and investigated as lubricant additives. U.S. Pat. Nos. 2,951,040; 3,419,589; 3,840,463; 4,966,719; 4,995,996; and 4,978,464 are representative of patent specifications describing both molybdenum and sulfur.
Molybdenum compounds for use as lubricant additives described in the art are principally dinuclear molybdenum compounds, characterised by the oxidation state Mo(V). However, International Patent Application No. PCT/IB97/01656 describes use of trinuclear molybdenum compounds as lubricant additives, i.e. characterised by a different oxidation state (Mo(IV); trinuclear molybdenum compounds have improved properties as lubricating additives compared with dinuclear molybdenum compounds as evidenced by test results in the above International Patent application, thus ameliorating the problem of providing improved lubricant performance in response to demands from original equipment manufacturers (OEM's).
The present invention provides tungsten analogues of the aforementioned trinuclear molybdenum compounds that are useful as additives in lubricating oil compositions.